1822.] produced hy Electricity, 7 



VI. I tried to make a comparison between the conducting 

 powers of fluid menstrua and charcoal and those of metals. Sis 

 inches of platinum foil, an inch and one-fifth broad, were placed 

 in a vessel which could be filled with any saline solution ; and 

 a similar piece of platinum placed opposite at an inch distance ; 

 the whole was then made part of a voltaic circuit, which had 

 likewise another termination by silver wires in water ; and solu- 

 tion of salts added, till gas ceased to be liberated from the nega 

 tive silver wire. In several trials of this kind, it was found that 

 the whole of the surface of six inches, even with the strongest 

 solutions of common salt, was insufficient to carry oft' the elec- 

 tricity even of two pair of plates ; and a strong solution of 

 potassa carried off" the electricity of three pair of plates only ; 

 whereas an inch of wire of platinum of -^4r-o (as has been stated) 

 carried oft* all the electricity of 60 pair of plates. The gas libe- 

 rated upon the surface of the metals when they are placed in 

 fluids, renders it impossible to gain accurate results ; but the 

 conducting power of the best fluid conductors, it seems probable 

 from these experiments, must be some hundreds of thousand 

 times less than- those of the worst metallic conductors. 



A piece of well-burnt compact box-wood charcoal was placed 

 in the circuit, being ^^ of an inch wide by -p'^ thick, and con- 

 nected with large surfaces of platinum. It was found that 

 1 inch and -^ carried off' the same quantity of electricity as 

 6 inches of wire of platinum of -^^. 



VII. I made some experiments with the hope of ascertaining 

 the exact change of ratio of the conducting powers dependent 

 upon the change of the intensity and quantity of electricity ; but 

 I did not succeed in gaining any other than the general result, 

 that the higher the intensity of the electricity, the less difficulty 

 it had in passing through bad conductors ; and several remark- 

 able phaenomena depend upon this circumstance. 



Thus, in a battery where the quantity of the electricity is very 

 great, and the intensity very low, such as one composed of plates 

 of zinc and copper, so arranged as to act only as single plates of 

 from 20 to 30 feet of surface each, and charged by a weak mix- 

 ture of acid and water. Charcoal made to touch only in a few 

 points is almost as much an insulating body as water, and cannot 

 be ignited, nor can wires of platinum be heated when their dia- 

 meter is less than ^ of an inch, and their length three or four 

 feet ; and a foot of platinum wire of -^-^ is scarcely heated by 

 such a battery, whilst the same length of silver wire of the same 

 diameter is made red hot; and the same lengths of thicker wires, 

 of platinum or iron are intensely heated. 



The heat produced where electricity of considerable intensity- 

 is passed through conductors, must always interfere with the 

 exact knowledge of the changes of their conducting powers, as 

 is proved by the following experiment: A battery of 20 pair of 

 [/ pltites of zinc, and copper plates 10 inches by 6, was very highly 



